This invention relates to a brake assembly for an off-highway truck, such as earthmoving trucks or the like, and, more particularly, a wet brake assembly joined to a wheel spindle by a mechanical spline joint.
Large off-highway trucks, such as earthmoving trucks having 240 ton hauling capacity, typically have at least a pair of wheels that are rotatably mounted on corresponding wheel axles or wheel spindles. These trucks use multiple disc brake assemblies for braking. These multiple disc brake assemblies include a plurality of rotatable and complementary non-rotatable discs that contact each other when the truck is braked to overcome the truck""s high momentum forces and stop or reduce the truck""s speed. Given the large size of the off-highway truck, and associated wheels that can have approximately 12 foot diameter tires, the brake assemblies experience very high loads and generate a great amount of heat during braking. Therefore, wet brake assemblies are typically used that are cooled by a fluid such as oil or other common fluid.
Known multiple disc brake assemblies include a brake anchor that is axially mounted on the wheel spindle and secured to a brake anchor flange that is integral with the wheel spindle at an inboard end of the wheel spindle. A large number of retention bolts are passed through the brake anchor flange and into the back of the brake anchor to form a mechanical bolted joint between the brake anchor and the brake anchor flange so that these two components are coupled in a non-rotatable manner. Upon braking, the mechanical bolted joint is subjected to high shearing forces that may cause undue shear stresses. In order to withstand these high shearing forces, the mechanical bolted joint must have a high shearing capacity. To achieve this, the brake anchor flange has a relatively large surface area where it couples with the back (i.e., inboard side) of the brake anchor, and the retention bolts are accurately tightened with a predetermined torque to create a high normal reaction force between the brake anchor flange and the abutting face of the brake anchor. The friction between the large surface area of the brake anchor flange the abutting face of the brake anchor, together with the normal load therebetween, determine the total shearing capacity of the mechanical joint.
The requirement for the brake anchor flange to have a large surface area to achieve the desired shearing capacity results in a large diameter flange that is relatively thin, making the spindle difficult to manufacture. In particular, if the spindle is cast, maintaining the flat shape of the brake anchor flange during casting and subsequent cooling is very difficult, given the brake anchor flange""s relatively large diameter. On the other hand, forging is difficult due to the large increase in the spindle cross-section at the large diameter flange.
Additionally, the large diameter of the brake anchor flange makes it susceptible to standing waves that can develop due to shocks received during operation of the truck by the wheel that are then transmitted through the spindle to the brake assembly. These standing waves cause excessive noise and vibration in the spindle and brake assemblies.
The large number of retention bolts required to create the necessary normal reaction force between the brake anchor and the brake anchor flange requires the bolts to be interspersed between components of the brake assembly, such as springs for the parking brake, and hydraulic ports in the brake anchor so as not to interfere with these components and ports. However, the available space for interspersing these retention bolts is limited, making it difficult to accommodate all the retention bolts. Accordingly, the brake anchor is typically increased in width to accommodate the length of the retention bolts without interfering with other parts of the brake anchor. Moreover, given that each of the retention bolts must be accurately tightened to create the necessary normal reaction force, sufficient clearance must be left on the back side of the brake anchor flange to allow a technician access to the retention bolts to carry out this labor intensive activity. Additionally, if the technician fails to accurately tighten the retention bolts, the shearing capacity of the mechanical joint may not withstand the operational shearing loads.
The multiple disc brake assemblies of off-highway trucks generate a relatively large amount of heat when braking. Hence, a number of off-highway trucks have heretofore been designed with fluid-cooled or wet brake systems. Such wet brake systems circulate lubricating oil around the discs of the disc brake assemblies, thereby cooling the discs during operation of the off-highway truck. However, there remains a need to increase the brake capacity, which can be achieved in three principle ways, namely, increasing the diameter of the brake discs, by increasing the number of these discs, and increasing the brake application force. Current design constraints limit the availability of these alternatives. One such constraint is the limited available space. In particular, increasing the brake size to allow for more brake discs reduces the spread between the two sets of wheel roller bearings required for rotatably mounting the wheel to the spindle.
The present invention is directed to overcoming one or more of the problems described above.
According to one aspect of the present invention, a brake assembly for braking a wheel is provided, having a brake anchor including a brake anchor first annular portion, a brake anchor second annular portion, a plurality of brake anchor splines on the brake anchor first annular portion.
According to another aspect of the present invention, a wheel spindle is provided for mounting a wheel and brake assembly, having a roller bearing assembly for rotatably supporting a wheel and a large diameter portion inboard of the roller bearing assembly having a plurality of wheel spindle splines on an outside circumferential surface of the large diameter portion.
According to yet another aspect of the present invention, a combination brake and wheel spindle is provided, having a wheel spindle, including a large diameter portion having a plurality of wheel spindle splines on an outside circumferential surface of the large diameter portion; and a brake assembly. The brake assembly includes a brake anchor, a brake anchor inboard annular portion on an inboard side of the brake anchor, a brake anchor outboard annular portion on an outboard side of the brake anchor, and a plurality of brake anchor splines on the brake anchor inboard annular portion. The brake assembly is axially mounted on the wheel spindle, and the plurality of wheel spindle splines are meshed with the plurality of brake anchor splines to form a mechanical spline joint so that the brake anchor is non-rotatably coupled to the wheel spindle.